Here is the full list of all 27 Hollow achievements.
Slain first wanton.
Kill wanton with single shot in a head.
Collect all available weapons.
Find all documents and notes.
Find all girl posters.
Find all collectable radios.
Sync all generators.
Fire-off all hands of wanton, than finish it with a headshot.
Kill wanton using gas tanks only.
Slain first Puker.
Slain first flying enemy.
Blow first destructible using gas tank.
Get killed more than 50 times.
Kill all monsters available in a game.
First bullet for Reaper.
Get caught by Reaper.
Finish Hollow game.
Unlock ending A.
Unlock ending B.
Finish game at HARD difficulty.
Finish game at HARD difficulty under 3 hours and do not use Save Discs.
Encounter Reaper for the first time.
Fix generator with fuse.
Go trouth all hallucination events in Laboratories.
Escape planet dream and get back to Shakhter-One deck.
Find way out of Cable Maze.
Kill burning Puker.